Guinevere is talking about being seduced on the way to her wedding...
...might that have been Arthur's first clue that the marriage was headed for trouble.
Remember he was a stranger, in the woods, when they first met.
I think it's a reference to the time period in which the tale is set. Remember those were fairly lawless times in a lot of ways. Thieves and other criminals had an easier time of it than a criminal would today. She had no means of communication and had slipped away from her protectors. Anything could happen to a woman back then in that set of circumstances.
It was a reference to the time period, but not in the sense of the objective reality of that past, but of the cultural past, or past as seen through culture. The Arthurian legends were incorporated and developed by the literary movement of courtly love (in a version of the song Guenevere sings while in the carriage - I don't know if it's from the film, or from the play, I've found the lyrics online - she mentions wanting to be set up on a pedestal and being worshiped by men, a motive clearly reminiscent of the imagery of courtly love, where the loved woman is exalted as unattainable - which, of course, as any economist would say - makes her even more desirable).
She was on her way to her arranged marriage, where she was to be married to the king of England, a powerful man. She did not know him, and we may presume that all she knew about him was this. It's a rather scary situation to be in, I assume. Yet she yearned to find love, even if from a stranger in the woods, provided he rescues her from the scary king (and be handsome - the king, from what she presumably knew, possibly wasn't). She wasn't fearing what may happen in the woods, she was hoping to escape an imposed marriage, void of love.